Many television receivers include a tuning memory for storing tuning information for active channels. For example, tuning memory may store a list of active channels, i.e., channels for which valid RF television signals are present. Channels not in the list will be "skipped over" during a channel scanning type of channel selection operation. The tuning memory may also store other information such as for precisely tuning each active channel.
The process of manually entering information into the tuning memory (or "programming" memory) may be very time consuming, especially when there are a large number of active channels. Accordingly, some television receivers provide an "auto-programming" feature for automatically entering information into the tuning memory.
During the auto-programming mode, each of the channels is successively selected for tuning until all the active channels are located. The determination of an active channel is made by a detector responsive to a signal indicative of the presence of a valid RF television signal. For example, the detector may be responsive to the characteristics of the IF signal produced by the tuner or to the video signal produced by the video detector.
RF signals received by a television may be broadcast RF signals having carriers with standard frequencies assigned by the Federal Communications Commission (FCC) or other RF signals having carriers with non-standard frequencies which are not assigned by the FCC and which may be offset in frequency from respective standard frequencies. Non-standard RF signals may be provided by cable frequency distribution networks and television accessories such as video tape machines, video disc players, video cameras, home computers and video games. Thus, most television receivers have provisions for tuning both standard frequency and non-standard frequency RF signals.
Tuning a non-standard frequency RF signal requires searching for the video carrier of the non-standard RF signal in a range surrounding the frequency of the video carrier of a respective standard frequency signal. This may be conducted under manual control by the viewer or automatically utilizing one or more signal detectors for identifying the presence of a valid RF television signal.
U.S. Pat. No. 4,405,947, entitled DUAL SEARCH MODE TYPE TUNING SYSTEM, issued in the names of J. Tults and M. P. French on September 1983 discloses a phase loop tuning system for automatically tuning non-standard frequency (as well as standard frequency) RF signals. Basically, for any selected channel, the frequency of the local oscillator signal under phase locked loop control is changed in a number of small steps in a frequency range corresponding to the frequency range of possible non-standard frequency RF signals until a detector indicates that a valid RF television signal has been properly tuned.
Auto-programming provisions which locate non-standard frequency RF signals can readily be added to the type of television receiver disclosed in the Tults et al. patent by utilizing the same search routine for each channel during the auto-programming mode as during the normal channel selection mode.